DE19742055C2 - Device for testing circuit boards - Google Patents

Abstract

An instrument to test electronic components, the instrument including a drive unit electrically connecting the component and electrically driving the component to generate a field in the nearby space. The instrument also includes a test device electrically insulated from the component and mounted in its vicinity in order to measure the field generated by the component. The drive unit is designed to apply a voltage to the component. The test device includes an instrument amplifier measuring the voltage differential of two electrodes positioned at two sites in the electric field generated by the component. One of the electrodes is positioned near the component.

Description

The invention relates to a device of the ge in the preamble of claim 1 called Art.

A device of the generic type is known from US Pat. No. 5,254,953 A. The first electrode and the component to be tested serve as plates nes capacitor, its capacity with the device by changing the charge is determined on the capacitor. To do this, the measuring amplifier must have a current Carry out the measurement in a connecting line between the first Electrode and the second electrode than that of the known generic  Device serves the mass of the circuit to be tested on a circuit board. The Measuring device is therefore galvanically connected to the circuit.

With this device components z. B. with an electric scarf PCBs are checked for correct assembly. Is that too bad? continuous component z. B. due to insufficient soldering or wire break not properly contacted, so only the much smaller capacity towards more distant components, e.g. B. the supply line, beyond the interruption.

The advantage of the generic devices is that the galva is not required African, ie mechanical contact between the first electrode and the Component. There are no good conductive contact surfaces on the component required. Oxide layers interfere with e.g. B. not. Can also through insulating layers or non-conductive housings are measured.

Since the measuring distance is included in the measured capacitance, with an exact Po sitioning of the first electrode geometric deviations of the to be tested Component are determined, for. B. by bending, crooked assembly or the like. It is also possible to measure plug contacts that are only suitable for one size current contacting are designed and therefore not z. B. with a test plug me may be burdened with

A disadvantage of the known device is the capacitive measuring method for the charge shift on the capacitor current flow in the circuit before suspends. This current also flows regularly in more complicated circuits through other components, their possible error deviations in the knife result. Since the measuring amplifier the current against the circuit ground determined, there is also always a capacitance between the first electrode  and the circuit ground parallel to the measuring capacitance. This annoying parallel kapa but is usually larger than the measuring capacity, so that deviations in the parallel capacitance to mass cause larger deviations. Au In addition, a high level of measurement sensitivity is required to ensure the small deviation of the measuring capacity in the large total capacity (measuring capacity + much larger capacity against mass).

A generic test device is from DE 26 39 831 A. known. In this known device that is in a generic manner in the case of electrical loading by means of a stimulation device from the component ment generated field measured with a field probe. Serves as a field probe this known construction a coil that is exclusively based on the magnetic Field component of the electromagnetic field generated by the component speaks. However, magnetic fields are only generated when current flows in the component testifies. Consequently, the stimulation device must be designed so that under construction element a current flow is generated. This results in similar effects parts as in the capacitive measuring method described above. All neighboring th, also current-carrying components of an assembled circuit can z. B. disturb. Components that are incorrectly indicated for certain reasons closed and therefore cannot be traversed by electricity, can not to be tested at all. Furthermore, due to the design-related size of the coil the local resolution of the test procedure is limited.

The object of the present invention is to provide a generic type direction while maintaining the advantages of non-contact measurement with larger Detection sensitivity of deviations on the component to be tested  less sensitivity to other deviations in the circuit create.

This object is achieved according to the invention with the features of claim 1 solves.

In the device according to the invention, one is made with the two electrodes Voltage between two points in the electric field determined by the stressed component is generated. The generation of a magnetic field and thus current flow in the component is not required. It is therefore sufficient for the component or one occupied by components Contact circuit with only one conductor. It can be a DC voltage and thus a generated purely electrostatic field can be used. The two Electrodes form a field probe with which the field geometry around the component can be measured with high precision. You can use both electrodes or in front preferably an electrode adjacent to the component is moved. Near the field to be tested essentially depends only on this. Is the component z. B. due to insufficient soldering or wire break not connected to the stimulus voltage, there is strong field deviation that compared to the target state - z. B. determined by a previous one Measurement on a correctly working circuit board - are very easy to prove. Shape deviations on the component to be tested, e.g. B. imbalance, bending etc., can be detected very easily by the resulting field deviations become. Other components interfere little due to their geometrically distant position that has little influence on the field, especially when in the near field the component to be tested is measured. The measuring process does not generate emergency currents in the circuit and measurement errors caused thereby. How in the generic state of the art there is no contact with the scarf through the electrodes. No easily contactable surfaces are necessary.  

It can ge over insulated surfaces or through plastic housing will measure, e.g. B. inside an embedded in a plastic housing ICs. Since field asymmetries are recognized particularly well, it is very easy to solve the hitherto unsolved problem of detecting the wrong way of using the electrical system lyt capacitors. The stimulation device can separate voltages on Create component, e.g. B. DC voltages with which problems caused by Kon capacitors in the circuit are avoidable. There are also impulses, e.g. B. Change voltage of any frequency, usable. It can even be electrical Field are determined, which are about components in the intended Operation of the circuit results. Therefore, the device according to the invention also use as a function tester. The field probe according to the invention has one suitable geometric resolution, even the switching processes in the Be considered inside an IC.

The second electrode can be anywhere in the electrical field, e.g. B. far outside of the measuring location. Then only the first electrode from the measuring location is required to be moved to the measurement site. However, the characteristics of the An are advantageous saying 2 provided. If both electrodes are the component to be tested neighboring, so the electric field in the close range, in the very high field strength kedifferences exist, measured very precisely, without being influenced by Fields of other components.

In a very simple design, the field probe can be arranged at the end a shielded cable according to claim 3. It can be this enables field measurements with a geometric resolution of less than 1 mm.

The features of claim 4 are advantageously provided. This can help Measurements in the close range of components to be tested galvanic contact  with these can also be avoided in the event of positioning deviations that interfere would lead to galvanic contact with the circuit.

According to claim 5, the first electrode can advantageously also have several components capture elements simultaneously. With suitable stimulation z. B. the individual construction elements one after the other, the other components, e.g. B. with the Stimulator are grounded with only one positioning of the first Electrode a larger number of components can be measured. This is ins especially in the case of geometrically and electrically essentially identical components ten advantageous, such as. B. with contact pins of a plug or at the final pins of an IC.

The stimulator can apply a DC voltage, the electrostatic cal field can be precisely measured by the device according to the invention. Before however, a pulsed voltage is partially applied according to claim 6, e.g. B. a pulsed DC voltage or an AC voltage, which is from the Meßver is more detectable.

In this case, pulse sequences of low frequency are advantageously used det, which are outside the usual frequency range, in the neighboring Radiate measuring devices and computers.

A triangular shape is preferably used as the pulse shape turns. This has the advantage that it increases the capacities of the measuring arrangement Rectangles are differentiated, which can be better processed by the measuring amplifier are.

Preferably, the measuring amplifier suppresses DC voltage according to claim 9 nung. Electrostatic fields, such as z. B. by electrostatic charge in  the vicinity of the measurement location can arise and which can lead to incorrect measurements are suppressed.

Preferably, the measuring amplifier is designed in such a way that it suppresses occurring interference frequencies, e.g. B. Grid frequencies in the 50th Hertz range, which are generated by neighboring power supplies or other interfering frequencies that are emitted in the vicinity of the measurement site, for. B. through computer CPUs in the 100 megahertz range, from robot control motors and the like.

The invention is described below with reference to the schematic Figures explained using exemplary embodiments.

Show it:

Figures 1a and 1b. The test of a contact pin for proper soldering to a conductor track,

Figs. 2a and 2b: the test of two parallel conductors on interruption of the conductor tracks,

Figures 3a and 3b: the test location of an electrolytic capacitor for correct installation.

Fig. 4: a field probe according to the invention in training at the end of a shielded line with positioning device and

Fig. 5 shows a field probe of the invention to test all pins ei nes ICs in only one positioning position.

Fig. 1a shows in section a typical test situation on a non-conductive Plati ne 1 , on which a metal pin 2 , z. B. one of several pins of a plug-in contact strip is attached, which is contacted with a conductor 3 on the circuit board by a solder 4 .

On the conductor track 3 at a suitable contact point 5 with a stimulating device 6, a voltage, for. B. a DC voltage of a few volts, with a contact tip 7 , which is shot at a voltage source 8 is. With the second contact tip 9 of the voltage source 8 , a Lei ter 10 is contacted, which is at a distance from the conductor track 3 . The conductor 10 can be earth, mass of the circuit located on the circuit board 1 or even a field plate that is suspended somewhere freely in the room.

Between the conductor 10 and the conductor track 3 and the elements electrically connected to it, such as in particular the component to be tested in the form of the pin 2 , an electric field is formed in the surrounding space. If the conductor 10 is far away from the components 2 and 3 , an essentially undisturbed electrical field is formed around the latter, the field (force) lines of which look approximately as shown in FIG. 1a.

It can be seen that the field lines are always perpendicular to the conductors 2 , 3 . At the ends of the conductors, i.e. at the tips of the conductors, the lines run divergently. On elongated pipe sections they run essentially parallel to one another.

FIG. 1b shows the same arrangement, but in the absence of soldering. 4 The pin 2 is electrically isolated from the conductor track 3 here. The voltage applied by the stimulation device 6 to the conductor track 3 is not applied to the pin 2 . The pin 2 is therefore only exposed as a conductor in the electrical field. It influences the field slightly due to influence, i.e. charge shifts on pin 2 . As shown, there is a completely different design of the field lines in the area of the pin 2 . In particular, the strong divergence in the area of the upper tip of the pin 2 is missing.

If a field probe with an electrode 11 , as shown, is arranged adjacent to the pin 2 in the same geometrical arrangement in the cases of FIGS. 1a and 1b, it sees completely different field strengths in the two cases shown in FIGS. 1a and 1b. This enables the error shown (missing solder joint 4 ) to be demonstrated. Are there other errors, such as an electrically insulating break in pin 2 , e.g. B. within the board 1 , or z. B. a break in the conductor track 3 , there are similar effects strongly distorting the electric field, which lead to reliable detection of the error.

Since the geometry of the measurement site is very closely involved in the measurement result, a geometrical deviation of the pin 2 can also be detected with exactly reproduced spatial positioning of the field probe 11 relative to the circuit board 1 , e.g. B. a bending of the pin, a short length or the like.

The field probe shown can with its electrode 11 z. B. be formed as a field plate, which is connected via a line 12 to an input of a measuring amplifier 13 . With a second line 14 , the other input of the measuring amplifier 13 is connected to a second electrode in the form of a field plate 15 which is arranged somewhere else in the room. If the first electrode 11 and the second electrode 15 are far apart, the electric field in the near field of the pin 2 is determined solely by the positioning of the first electrode 11 , while the second electrode 15 is preferably in one of the circuitry on the circuit board 1 undisturbed area. The dipole formed by the electrodes 11 and 15 can, however, also be formed in a very small space, that is to say with closely adjacent, very small electrodes 11 and 15 , and then determines the local field strength at the location of the field probe 11 with high precision. Since such a dipole measures direction-dependently, that is, in the direction of the field lines shown it has a higher sensitivity than transverse to it, the direction of the field lines can be determined and thus the electric field can be detected very precisely.

FIGS. 2a and 2b show another typical measurement problem on the circuit board 1, which this time is shown in plan view. Two conductor tracks 20 and 21 lie in parallel and are subjected to a voltage difference by the stimulation device 6 . An electric field with parallel field lines forms between them, as shown in FIG. 2a. This can be determined at the point shown with the electrode 11 of the field probe, which can speak ent of the rest of FIG. 1.

In Fig. 2a, the conductor track 21 with a break 22 is divided into the two sections 21 a and 21 b. Only the section 21 a is acted upon by the stimulation device 6 , while the separated section 21 b is free of tension.

As shown in FIG. 2b, this leads to a strong change in the electrical field, as the field lines shown indicate. This strong deviation in the electrical field can easily be recognized by the field probe 11 in comparison with the measurement in FIG. 2a on a properly manufactured circuit board.

FIGS. 3a and 3b show an extraordinary difficult test case on the circuit board 1 (shown in section), namely, an electrolytic capacitor 30, which is shown for illustrative purposes in a highly schematic older design.

The electrolytic capacitor 30 has an outer cup-shaped electrode 31 forming the housing, which is contacted with a feed line 32 and an inner electrode 34 contacted with a feed line 33 .

The electrolytic capacitor 30 is provided in the correct installation position in FIG. 3a. In Fig. 3b he is sitting the wrong way round, that is, with reversed polarity. This must be recognized by the test device.

For the test, the capacitor 30 is subjected to voltage in both cases, by contacting the leads 32 and 33 with a stimulating device, not shown, z. B. The stimulation device 6 of FIG. 1. This results in the vicinity of the electrolytic capacitors 30 in each case an electrical field with field lines, as shown in FIGS . 3a and 3b. It is known that the field lines in the region of the electrolytic capacitor 30 , in which the lead 33 is contacted with the inner electrode 34 , emerge with a high density, that is to say a high field strength, from the opening of the shielding cup-shaped outer electrode 31 at a distance from it However, there is a very low field strength. Is adjacent in the same geometrical arrangement in the two cases of FIGS. 3a and 3b, the aforementioned field probe 11 for electrolytic capacitor 30, the Figure results in the two cases shown. 3a and 3b, an extremely different measurement result is totally contrary to all other known test devices that result in the example shown of a wrongly installed electrolytic capacitor only very low measurement results. Several measurements with reversed stimulus polarity are not necessary.

FIG. 4 shows an example of a field probe with a spatially very small dipole, that is, the field geometry with a high resolution. The field probe is provided at the end of a shielded cable 40 . The two poles of the dipole are formed by the outer shield 41 and the inner conductor 42 protruding from the end of the shielded cable 40 . If a very thin shielded cable with a total diameter of less than z. B. 1 mm used, a dipole field probe can be generated with a distance between the two poles in the range below 1 mm, with which electric fields can be measured with a correspondingly small geometric resolution.

Fig. 4 also shows a positioning device 43 , which is adjustable with a device not shown in the three spatial directions shown and with an arm 44 and a bracket 45 carries the end region of the shielded cable 40 , ie the field probe. With the positioning device 43 , the Feldson de can be positioned precisely in the electrical field around components.

The shielded cable 40 is connected at its end facing away from the field probe with its shield 41 and its inner conductor 42 to the two inputs of the measuring amplifier 13 already mentioned, which also determines the voltage between the electrodes 42 and 41 , its input having to be very high-resistance in order to not to burden the field too much.

Fig. 5 shows a perspective view of a commercially available IC 50 with connection pins 51 , which are arranged in a row. It is to be tested whether the pins 51.1-51.6 are properly soldered to conductor tracks 52 of the circuit board 1 , it being possible for the soldering points to be designed corresponding to the soldering points 4 in FIG. 1a.

Pin 51.4 is currently being tested for proper soldering. It is applied the stimulus means already described 6 which contacts with a contact tip 7, the conductor track to the pin 51.4 and all other interconnects connecting with its other pole with vain series of parallel contact tips 9.1-9.5 52 to the other pole of the voltage source. 8 A voltage is therefore applied to pin 51.4 against all other pins.

In the exemplary embodiment in FIG. 5, the test device has two electrodes 53 and 54 , which are separated by insulation 55 and are connected to the measuring amplifier 13 already discussed via twisted cables. As can be seen from Fig. 5, the two electrodes 53 and 54 extend over a large area over the entire IC 50 , so are all pins 51.1-51.6 equally adjacent. The electrical field generated by applying a voltage with the stimulation device 6 to the pins can be detected by the electrodes 53 and 54 and detected by the measuring amplifier 13 . As FIG. 5 shows, this essentially results in the same field with different wiring of the pins. Each of the pins 51.1-51.6 can thus be connected in succession to the contact tip 7 of the stimulation device 6 , all the other pins being connected to the contact tips 9.1-9.5 , that is to say the other output of the voltage source 8 . In this way, in the same way as described for FIGS . 1a and 1b, all pins 51.1-51.6 can be examined one after the other for proper soldering with their conductor tracks 52 . The electrode arrangement 53 , 54 does not need to be repositioned, which considerably simplifies the test procedure.

With the test setup according to FIG. 5, other similar structures can also be searched, for. B. standing in a row pins of a power strip and the like.

The measuring amplifier 13 described in the embodiments discussed must be designed to measure very small field strengths. So he must have very low voltages, e.g. B. in the µV range.

When designing the measuring amplifier 13 , it should be taken into account that there may be interfering external fields at the measuring location which overlap the field that is generated by the component to be tested. Such fields can e.g. B. Fre frequencies in the network frequency range, so z. B. originate from neighboring transformers. In addition, adjacent computers can have very strong interference in the area of e.g. B. generate 100 megahertz. Such known interference frequencies can be suppressed by suitable filter devices in the measuring amplifier 13 .

But there may also be strong DC interference, e.g. B. by electrostatic fields, which come for example from electrostatic charging. Since the measuring amplifier 13 advantageously also suppresses DC voltage.

With DC voltage suppression at the measuring amplifier 13 , the field to be measured, emitted by the component, must be pulsed. The stimulating device 6 is designed to apply pulses, the voltage pulses in the form of DC voltage. AC voltage pulses or as a sinusoidal AC voltage can be used. These then preferably have frequencies in the lower frequency range, i.e. below z. B. 100,000 Hz, since fewer interference frequencies occur in this low frequency range.

In a particularly preferred embodiment, the stimulation device 6 supplies triangle pulses which, after differentiation in capacitances in the measurement setup, result in rectangular pulses which are particularly easy to detect by the measurement amplifier 13 .

If, for example, the field probe shown in Fig. 4, which is suitable for very small-scale measurement of the electric field, in the vicinity of a component to be tested, for. B. the pin 2 in Fig. 1a, and the field is to be determined in the immediate vicinity of the component, it can come to incorrect positioning of the electrode 42 with the pin 2 in the event of incorrect positioning. This would lead to incorrect measurements. Therefore, in a manner not shown, this electrode or both electrodes 42 and 41 can be provided with an insulating coating that does not interfere with the field measurement, but prevents electrical contact.

Claims (10)

1. Device for testing electronic components ( 1 , 2 , 21 , 30 , 51.4 ), with a stimulation device ( 6 ) which is galvanically contacted with the component and this stimulates electrical build-up to build up a field in the surrounding space, and with a measuring device which is galvanically separated from the component and is arranged in the vicinity thereof for measuring the field generated by it, characterized in that the stimulating device ( 6 ) for applying a voltage to the component ( 1 , 2 , 21 , 30 , 51.4 ) is formed and that the measuring device has a measuring amplifier ( 13 ) which measures the electrical voltage difference between two electrodes ( 11 , 14 ) which are positioned at two points in the electrical field generated by the component, and of which a first Electrode ( 11 ; 42 ; 53 ) is positioned in the vicinity of the component. 2. Device according to claim 1, characterized in that the two electrodes ( 41 , 42 ) are arranged at a short distance from one another from the order of magnitude of the structure of the component to be tested. 3. Apparatus according to claim 2, characterized in that an elec trode through the shield ( 41 ) of a shielded cable ( 40 ) and the other electrode is formed by its protruding over the end of the cable inner conductor ( 42 ). 4. The device according to claim 1, characterized in that at least the first electrode ( 11 , 42 , 53 ) is provided with a galvanic contact-preventing insulation. 5. The device according to claim 1, characterized in that the first electrode ( 53 ) is formed over a large area several components ( 51.1-51.6 ) überec kend. 6. The device according to claim 1, characterized in that the stimu liereinrichtung ( 6 ) applies a pulsed voltage. 7. The device according to claim 6, characterized in that the pulse fol corresponds to a frequency below approximately 100,000 Hz. 8. The device according to claim 6, characterized in that the pulses Have a triangular shape. 9. The device according to claim 6, characterized in that the Meßver suppresses ( 13 ) DC voltage. 10. The device according to claim 6, characterized in that the Meßver stronger ( 13 ) suppresses interference frequencies.